I am interested in learning English is correct. The choice of using which preposition can be difficult. I suggest that you learn it in phrases. Thus interested in putting on as in putting on my clothes getting on with as in how are you getting on with your lessons?

I am interested in learning English. - IN is used when you are referring something enclosed by limitations while using IN is relatively specific and does not denote anything enclosed. - ON is used to denote a position for surfaces or a position just above or outside an area. Also, ON is used with street names. Conversely, IN is used with names of cities, towns, provinces, states, and countries.

it is right with "I am interested in Learning English"....Have good time.